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Twins Researcher Delivers Outstanding Professor Lecture April 17
Twins study scholar examines how environment affects behavior by studying children who were adopted by parents who also have children of the same age.

April 6, 2006 :: No. 201
by Mimi Ko Cruz

Already known worldwide for her research on identical twins, psychology professor Nancy L. Segal now is studying unrelated “twins.”

Segal calls them virtual twins because they are not genetically related but, like twins, they are close in age and reared together from infancy.

“It’s the reverse of identical twins raised separately,” said Segal, who was named Cal State Fullerton’s Outstanding Professor in 2005. “I’m studying children who were adopted by parents who also have biological children the same age or other adopted children the same age. It’s a wonderful way to discover how environmental factors affect behavior.”

The study is ongoing, and Segal plans to discuss it at her April 17 Outstanding Professor Lecture. Set for 11 a.m. in the Titan Student Union, “Twins & Virtual Twins: Insights Into Human Behavior” is open to the public.

Segal, a fraternal twin herself, will describe the logic behind twin research, and discuss findings and implications from her studies in which she has examined a range of human behavioral and physical traits, including intelligence, social relationships, athleticism and sexuality. She also will share insights from her 2005 book, “Indivisible by Two: Lives of Extraordinary Twins,” and offer speculation on where twin research is headed in the future.

“Nancy defines outstanding professor for me,” said Thomas P. Klammer, dean of the College of Humanities and Social Sciences. “I especially admire how she involves her grad and undergrad students in research that moves the field of behavioral genetics forward and makes Cal State Fullerton well known in twins research worldwide. Everyone finds her work fascinating.”

Segal joined the Cal State Fullerton faculty in 1991 as an associate professor and established the Twin Studies Center the same year. She was promoted to full professor in 1994 and her first book, “Entwined Lives: Twins and What They Tell Us About Human Behavior,” was published in 1999. She’s also written more than 80 scientific papers in scholarly, peer-reviewed journals.

Among her research that has been cited in scores of publications is the Minnesota Study of Twins Reared Apart, a project with which Segal has been associated for many years. She and her colleagues found striking similarities between the separated identical twins, despite their different home environments. Many of the twins held similar jobs, had similar mannerisms, liked the same kinds of food and entertainment, and frequently felt an immediate bond upon first meeting. The separated fraternal twins generally showed much less resemblance.

In “Entwined Lives,” Segal wrote: “Twin research is not solely about twins, it is a model that helps all of us find answers to questions of who we are and how we got there.

“Twin studies are assisting discoveries into the bases of human intelligence and personality and the genetic components of complex diseases, such as multiple sclerosis and schizophrenia,” she wrote.

“Economists use twins to uncover ability and educational factors affecting annual income, and psychologists are recruiting multiples to explore the foundations of human happiness, marital satisfaction and love styles.”

Her own research findings have even influenced legal decisions in wrongful death, injury and custody cases involving twins.

In “Indivisible by Two,” Segal tells the stories of a dozen sets of twins, triplets and quadruplets. They include the twin brothers who were raised separately, yet both became firefighters; twin sisters who overcame one twin’s infertility by having the other serve as a surrogate mother; the pair that started out as identical sisters, then one was surgically transformed into a man; identical triplet brothers, one of whom is gay while the others are heterosexual; identical brothers who married identical sisters; Chinese twins adopted by different Canadian families yet raised as sisters; twin survivors of Josef Mengele’s gruesome experiments in Auschwitz; and twin brothers born in the 1930s to a Jewish father and a German gentile mother — one was raised as a Jew in Trinidad and the other as a Catholic who became a Hitler Youth member in Nazi Germany.

One of Segal’s current studies includes an Internet survey in which she is comparing the social relationships of families with twin parents. She is asking whether identical twins are socially closer to their nieces and nephews than are fraternal twins, and whether they give them a great number of gifts. Her students are processing the data, and results will be analyzed as early as next month.

“Everybody is fascinated by twins,” Segal said. “The idea of two identical people is just not what we expect and yet it happens. Research using twins helps us learn why we are the way we are and what it means to be human. This is why I’m so eternally fascinated.”

The Outstanding Professor Lecture is sponsored by the President’s Office, President’s Associates, Office of the Vice President for Academic Affairs, Academic Senate and the Faculty Development Center.

Media Contacts:

Nancy L. Segal, 657-278-2142 or
Mimi Ko Cruz, Public Affairs, 657-278-7586 or

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Nancy Segal
Nancy L. Segal

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